It's always important to compare the whole economy, not just a single number. For context, the median income in 1940 was $18680 in 2021 dollars ($956 in 1940, https://www.npr.org/2012/04/02/149575704/the-1940-census-72-...)

So in terms of the income of the average US man[1] in 1940 the WW2 cost was double the nominal number alone.

[1] The source above explicitly says man, not person, so presumably the median household income was even less than half of today's numbers.